In a conventional crawler for game mounted with a storage battery, when charging of the battery becomes necessary, the crawler is taken out from a game apparatus and the storage battery is connected to a charger for charging in a state that the storage battery is mounted on the crawler, or the storage battery is taken out from the crawler.
However, since the crawler is disposed within a closed space under a runway surface, it is troublesome and difficult to take out the crawler outside. Therefore, the charging takes much labor and time.
When the crawler is housed in a game apparatus, whether the storage battery needs charging or not can not be foreseen. Therefore, the storage battery must be charged early before the crawler becomes not able to self run during game. As the result, life of the storage battery is short because the number of times of charge of the storage battery is limited.